The invention relates to a method for the mechanical removal of a layer of alien material from a basic material of a disc-shaped information carrier, in particular an optically readable information carrier. The invention also relates to a device for carrying out this method.
High-quality synthetic resins, for example polycarbonate, are used in the manufacture of disc-shaped information carriers with a high storage density, for example optically readable digital audio discs (CDs) because of the high requirements imposed on the dimensional stability of such discs. The reject rate in the manufacture of such information discs is comparatively high in practice. To reduce waste, the basic material for the disc-shaped information carrier, usually polycarbonate, is recovered. This is done in a recycling process in which the polycarbonate is once more used in granulate form for the manufacture of the disc-shaped information carriers. To achieve this, the alien materials present on the basic material of the information disc must be removed in a reliable manner in order to achieve the purity required for re-use.
The layer of alien material present on the basic material of the information disc usually comprises a thin aluminum layer lying on the basic material, a radiation-cured acrylate lying on the aluminum layer, and one or several layers of colored print lying on the acrylate.
A method of the kind mentioned in the opening paragraph is known from, for example, DE 41 23 199 C2. In this known method, the layer of alien material is removed from the basic material by means of a material-removing cutting operation carried out parallel to the surface of the information carrier. This method requires a special machine adapted thereto. Furthermore, this machine must be so designed that the layers of alien material provided at the end faces of the information disc are also removed. The material losses may amount to up to 20% here.
The document cited above describes additional possibilities for removing layers from such information discs. It is thus possible, for example, first to dissolve the layer of alien material in a chemical process and subsequently to remove it. A disadvantage of this is the creation of a large quantity of dissolved wastes whose disposal involves much cost and effort. The cited document furthermore describes a mechanical process in which the layer of alien material is removed through the use of a jet of particles or an abrasive substance, which grinds off the alien material. Such a method is described, for example, in DE 38 16 651 C1 for the repair of damaged protective layers of a compact disc. This method is uneconomical owing to the loss of large quantities of blasting agents.
The brochure "GREEN TECH, Industriereinigung ohne Chemie" (Industrial Cleaning Without Chemicals) discloses a method and an appliance for cleaning of various materials, for example for cleaning metal, synthetic resin, stone, glass, or for cleaning electrical components. Dry ice (frozen carbon dioxide, CO.sub.2) is blasted onto the impurities by means of compressed air in this method. The carbon dioxide, concentrated into pellets of dry ice the size of a rice grain in a special process, works itself through the impurity during this. The polluted surfaces can be cleaned without residues very quickly in this way.
The above citations are hereby incorporated in whole by reference.